var calPoints = function(ops) { const points = []; ops.forEach(function(point){ console.log(points); const len = points.length; if (point === 'C') points.pop(); else if (point === 'D') points.push(2 * points[len - 1]); else if (point === '+') points.push(points[len - 1]+points[len -2]); else points.push(parseInt(point)); }) return points.reduce((a, b) => a + b, 0); }; calPoints(["5","2","C","D","+"]);